Magnetic relaxation phenomena in the superspin-glass system [Co80Fe20/Al2O3]10

Sahoo, Sarbeswar; Petracic, O.; Binek, Christian; Kleemann, W.; Sousa, J.B.; Cardoso, S.

doi:10.1088/0953-8984/14/26/312

Cited by 20 publications

(16 citation statements)

References 26 publications

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“…From the viewpoint of 1), we consider that the permalloy nanoparticle system studied by Sun et al is closer to a superparamagnet, while the Fe-N system studied in the present work and the Co-Fe nanoparticle system studied by Sahoo et al 30,31,37 are closer to a superspin glass. Lastly, we have argued that these two aspects peculiar to superspin glasses are qualitatively reproduced by the random energy model, and are well interpreted by the droplet theory in the field of the spin-glass study.…”

Section: Discussionmentioning

confidence: 64%

Aging and memory effects in superparamagnets and superspin glasses

et al. 2005

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Many dense magnetic nanoparticle systems exhibit slow dynamics which is qualitatively indistinguishable from that observed in atomic spin glasses and its origin is attributed to dipole interactions among particle moments (or superspins). However, even in dilute nanoparticle systems where the dipole interactions are vanishingly small, slow dynamics is observed and is attributed solely to a broad distribution of relaxation times which in turn comes from that of the anisotropy energy barriers. To clarify characteristic differences between the two types of slow dynamics, we study a simple model of a non-interacting nanoparticle system (a superparamagnet) analytically as well as ferritin (a superparamagnet) and a dense Fe-N nanoparticle system (a superspin glass) experimentally. It is found that superparamagnets in fact show aging (a waiting time dependence) of the thermoremanent-magnetization as well as various memory effects. We also find some dynamical phenomena peculiar only to superspin glasses such as the flatness of the field-cooled magnetization below the critical temperature and memory effects in the zero-field-cooled magnetization. These dynamical phenomena are qualitatively reproduced by the random energy model, and are well interpreted by the so-called droplet theory in the field of the spin-glass study.

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Section: Discussionmentioning

confidence: 64%

Aging and memory effects in superparamagnets and superspin glasses

et al. 2005

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“…1b), with peaks appearing at times close to the corresponding wait times similarly as observed in atomic spin glasses [8]. We have previously shown that the relaxation of thermoremanent magnetization exhibits similar aging phenomena albeit showing less clear correlations between t w and tðS max Þ [9]. Presumably this was due to non-linearity effects owing to comparatively large field steps applied.…”

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confidence: 63%

Non-equilibrium collective dynamics of a superspin glass

Sahoo

Petracic

Kleemann

et al. 2004

Journal of Magnetism and Magnetic Materials

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“…Also, the magnetization of the FC curve keeps increasing beyond the maximum of the ZFC curve. Thus, we may identify the temperature at which the maximum of the ZFC curve occurs as a superparamagnetic blocking temperature, T B , rather than a spin-glass-like freezing temperature [9]. To further confirm the absence of spin-glass-like aging phenomena, ZFC/FC data were also collected on a sample of dense (40 mg Fe 2 O 3 /ml) frozen ferrofluid, shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

Gummic acid stabilized γ-Fe2O3 aqueous suspensions for biomedical applications

et al. 2009

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Biomedical applications of magnetic nanoparticles depend critically on their preparation as aqueous colloidal suspensions, or ferrofluids, with long term stability under physiological conditions. Dispersion of the magnetic nanoparticles is generally achieved by the use of protein cages, polysaccharide, polypeptide and charged macromolecular coatings, which minimize interparticle magnetic interactions, particle agglomeration and precipitation. The synthesis and characterization of gummic-acid stabilized maghemite ferrofluids is reported. X-ray diffraction, transmission electron microscope and dynamic light scattering measurements give a γ-Fe 2 O 3 magnetic core diameter of 8 nm and a nanocomposite particle hydrodynamic diameter of 50 nm. Mössbauer and magnetization measurements indicate the presence of isolated, sterically stabilized superparamagnetic nanoparticles resistant to aging, and thus, promising agents for the production of novel magnetopharmaceuticals.

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Magnetic relaxation phenomena in the superspin-glass system [Co80Fe20/Al2O3]10

Cited by 20 publications

References 26 publications

Aging and memory effects in superparamagnets and superspin glasses

Aging and memory effects in superparamagnets and superspin glasses

Non-equilibrium collective dynamics of a superspin glass

Gummic acid stabilized γ-Fe2O3 aqueous suspensions for biomedical applications

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